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PROPERTY281 Test 1 > L8: HVAC > Flashcards

L8: HVAC Flashcards

1
Q

What does HVAC stand for?

A

Heating and humidification
Ventilation
Air conditioning and dehumidification

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2
Q

Is HVAC required?

A

Heating - yes

Cooling - no

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3
Q

What does HVAC achieve?

A

Temperature control
Humidity control
Air movement
Air filtration

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4
Q

What are the three categories that determine comfort?

A

Personal/physical
Measurable environment (RH, temp)
Psychological (air movement, noise)

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5
Q

What is relative humidity?

A

The ratio of moisture in the air compared with the maximum (100% means air cannot contain any more moisture at that temp - higher temp = more moisture)

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6
Q

What is the comfort envelope temperature and relative humidity?

A

Temperature 68-79ºF

RH targeted at 50%

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7
Q

What other factor is considered in the comfort envelope?

A

Clothing coefficient

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8
Q

What are the two thermal loading types?

A

Skin load dominated (outside - 55%)

Internal load dominated (outside - 20%; energy from people/lights/equipment dominate)

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9
Q

What are the three different sources of heat flow/gain through a building envelope?

A

Temperature difference
Solar radiation
Air infiltration

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10
Q

What is the R value?

A

Resistance to heat exchange = 1/k (1/conductivity)

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11
Q

What is the U value?

A

Thermal transmittance = 1/R1+R2+R3+…

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12
Q

What is the thermal gradient?

A

The gradual temperature change through the materials in the building envelope

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13
Q

How is the heat flow through building envelope calculated?

A

As the hourly conductive heat loss through the envelope based on area, temperature difference and U value

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14
Q

How is heat fain due to solar radiation calculated?

A

With complex calculations depending on type, shading, sunlight

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15
Q

How does angle of incidence affect light reflected?

A

Shallower angle = higher % reflected

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16
Q

What is heat flow by infiltration and what are the three most common causes?

A

Accidental influx of outdoor air

Floors, walls and ceilings, ducts, fireplaces

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17
Q

What are zones?

A

Area divisions within a building that operate separately

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18
Q

What are zones commonly based on?

A

Thermal loads - perimeter (changes with weather) vs core (always cold)

Use of space - tenants, different aromas, different operating hours

Quality of space - high quality gives independent control eg. hotel room, labs

19
Q

What are the 4 types of HVAC systems?

A

All-air
All-water
Air-water
Packaged

20
Q

What are the 4 types of all-air HVAC systems?

A

Single duct, constant air volume
Multi-zone, constant air volume
Single duct, variable air volume
Double (dual) duct

21
Q

What is single-duct CAV?

A

Constant temperature (cooled/chilled by water from chiller/boiler)
Low-velocity duct system
Master thermostat sets temp for whole building

22
Q

What is multi-zone CAV?

A

Allows separate temperature control (cannot change between hot/cold mode but can change how hot/cold with device that lets in small amounts of heat/coolth to adjust temp)
Separate ducts from AHU

23
Q

What is single-duct VAV?

A

Dampers at terminal outlets adjust air flow

More common/efficient than CAV

24
Q

What is double-duct?

A

Separate ducts for hot and cold air go to a mixing box where it is blended to reach the desired temperature providing unmatched comfort control
High velocity system to reduce duct size (less space)

25
Q

What is an all-water system and what are the two types?

A

Pipes carry hot/cold water to fan coil units; take air from room, heat/cool, replace

2 pipe and 4 pipe

26
Q

What is a 2 pipe system?

A

One supply and one exit pipe; whole building is either in heating or cooling mode

27
Q

What is a 4 pipe system?

A

Two supply and two exit (one hot, one cold); more variance as each fan coil can either be in heating or cooling mode irrespective of the others

28
Q

What do all water systems require and why?

A

Separate ventilation systems to change air because air is not being changed (just heated/cooled and replaced)

29
Q

What are air-water systems?

A

Air gets heated/cooled at fan room and then further heated/cooled when mixing with room air by fan coil unit

30
Q

What are packaged systems?

A

Self-contained systems for smaller scale buildings (rooftop units)
Split units - outside compressor and condenser, inside coils and fan

31
Q

What are 8 components in an HVAC system?

A

Chilled water plant (evaporator/chiller, compressor, condenser)
Cooling tower
Air handling unit (supply fan, air filters)
Boiler
Ducts
Diffusers/registers
Grills

32
Q

What do the components in the chilled water plant do?

A

Evaporator/chiller - liquid expands, cools, becomes vapour (Boyle’s Law) and cools water for AHU
Compressor - increases pressure
Condenser - cool condensing water turns vapour to liquid (warms condensing water)

33
Q

What does the cooling tower do?

A

Warmed water from condenser sprayed through air where it cools and returns to the condenser

34
Q

What does the air handling unit do in cooling/heating mode?

A 
Cooling mode:
Unconditioned air (used/outside) enters --> filtered --> passes over cooling coil (with chilled water from evaporator) and condensation drained --> conditioned air (lower temp and humidity)

Heating mode:
Unconditioned air –> filtered –> preheated –> passes over cooling coil (turned off) –> reheated –> conditioned air through ductwork –> humidifier sprays mist to add moisture if necessary

35
Q

What does the supply fan do and what are the two types?

A

Provides moderate air pressure to blow air through ductwork

Serial (propeller)
Centrifugal (offset and easier to access)

36
Q

What do air filters do and what are the three types?

A

Remove odours, irritants and pollutants

Arrestance - gauze/mesh traps particles; needs regular changing and can reduce air flow when clogged
Washing - incoming air sprayed so particles wash into collection tray; increases humidity and can cause bacteria
Electrostatic - particles magnetically drawn out; most effective

37
Q

What does the boiler do?

A

Produces hot water/steam used in air handling unit

38
Q

What are ducts typically made of and the two classifications?

A

Sheet metal

Low-velocity or high-velocity (>10ms-1)

39
Q

What do diffusers and registers do?

A

Supply air to spaces; diffusers have angled slates to distribute in various directions and registers have a grill and blades so supply air can be controlled

40
Q

What are grills?

A

An opening for air to return to the system

41
Q

How can ductwork be placed?

A

Vertically (core, structure, edges)

Horizontally (circulation paths, structure edges, plenum)

42
Q

What is the plenum and how does HVAC work there?

A

Space between ceiling and above floor deck

No ductwork; air pressurises in plenum space and displaced through openings in the ceiling

43
Q

What is typical cooling capacity and size of boiler/chiller room, cooling tower and fan room for a 15,000m2 high-rise?

A

Cooling capacity - 450tons
Boiler/chiller room - 300m2
Cooling tower - 60m2
Fan room - reaches max 25 floors

44
Q

What is heat flow measured in?

A

British Thermal Unit / hour or Watts

PROPERTY281 Test 1 (12 decks)

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